Endoscopes are widely used in the medical field and industrial field for capturing an image of an inside of a patient's body or capturing an image of an inside of a device or a structure. With regard to such endoscopes, it has been known to make a configuration such that, in an insertion portion of the endoscope that is to be inserted into an inside of an object to be observed, an objective lens system causes the light from a region to be imaged to be focused on a light receiving surface of an image sensor so that the light is converted to an electrical signal, which in turn is transmitted via a signal cable to an external image processing device or the like as a video signal. Such an insertion portion is required to have a sufficient sealing property for ensuring physical protection and waterproofness when the endoscope is used or at the time of maintenance.
In a case where the insertion portion of the endoscope includes a cover lens mounted to the distal end of the main body thereof so as to be exposed on an outer surface, for example, the sealing structure for the insertion portion of the endoscope may include a silicon-based bonding agent applied from an outer surface side to fill the space between the cover lens and the distal end of the main body to thereby prevent entrance of water or the like into an inside of the endoscope through the part where the cover lens is attached to the distal end of the main body (see JP3737848B2, for example).
In the conventional technology described in JP3737848B2, if a portion (excess portion) of the bonding agent applied to firmly fix the cover lens enters an optical path forming part (for example, an optical path between the cover lens and another lens disposed behind the cover lens) in the endoscope, a problem may arise that the bonding agent can interfere with the incident light (object image) traveling toward the image sensing device. To prevent the undesired entrance of the bonding agent, it may be conceived to reduce the amount of bonding agent applied or to use a bonding agent having a relatively high viscosity, but in these cases, it would become difficult to completely fill the gap between the cover lens and the distal end of the main body with the bonding agent, and this can result in a reduced sealing performance.
The present invention is made to solve the aforementioned problems in the prior art, and a primary object of the present invention is to provide an endoscope and an endoscope system which, in a structure where a light-transmissive closure member is fixed by a bonding agent to a distal end (front) opening of an insertion portion that is to be inserted into an inside of an object to be observed, can prevent entrance of the bonding agent into an optical path forming part defined at the rear of the closure member without reducing the performance of the bonding agent to seal the opening.